With the trend toward compact and lightweight electronics, soft-packaging batteries have been extensively used in consumer electronics such as iPhone, iPad, Ultrabook and so on, and are further expected to be used in cell-driven vehicles or scooters and energy storage devices.
A common lithium battery typically uses an aluminum plastic film packaging material (hereinafter referred to as the APF packaging material). For preventing water (H2O) from acting with lithium hexafluorophosphate (LiPF6) in electrolyte to form hydrofluoric acid (HF) that can corrode aluminum foil and lead to a short circuit and even explosion of the battery, anti-corrosion treatment is necessary. Such anti-corrosion treatment for aluminum foil usually involves applying hexavalent chromium (Cr6+) to the aluminum foil surface by means of coating or impregnation.
Besides, since nylon film is not resistant to electrolyte, in the event that electrolyte overflows during fill operation, the outmost layer of the packaging material tends to be corroded and whitened, the outmost material is preferably made by laminating a general polyester film with a nylon film for better protection.
For addressing the needs, some prior-art solutions have been proposed and are named bellow:
US Patent Publication No. 2015/0104698 discloses a packaging material for lithium batteries and a method for making the same. The packaging material has water, high temperature and corrosion resistance, and comprises a substrate layer, a binding layer, an aluminum foil layer, an anti-corrosion layer, an adhesive layer, and an inner layer. The prior-art device has aluminum foil applied with a conductive coating material act as the anti-corrosion layer. The adhesive layer with water, high temperature and corrosion resistance is made by mixing a OH-containing modified fluorocarbon resin and polyol, reacting the mixture with isocyanate to produce a fluorinated polyurethane polyol, and blending the fluorinated polyurethane polyol with a heat-resistant bisphenol epoxy resin to form a joint adhesive that has an interpenetrating network structure to be used in the packaging material for lithium batteries.
US Patent Publication No. 2010/0255365 discloses a packing material for a lithium cell, which has a first adhesive layer, an aluminum foil layer, a coating layer, an adhesive resin layer or a second adhesive layer, and a sealant layer laminated sequentially on one surface of a base material layer. The coating layer is a multilayer structure comprising a layer (A), in which 1 to 100 parts by mass of a phosphoric acid or a phosphate has been blended into 100 parts by mass of a rare earth element-based oxide, and a layer (X) which contains an anionic polymer and a cross-linking agent that causes cross-linking of the anionic polymers.
While the packing material for a lithium battery so produced has its resistance to hydrofluoric acid (HF) or solvents satisfying to the battery cell industry, with the enforcement of the EU's RoHS, WEEE and REACH, the use of hexavalent chromium (Cr6+) is forbidden in more and more jurisdictions, and some European countries as well as the US have planned to fully prohibit the use of hexavalent chromium and other heavy metals in the future. Besides, the manufacturing of the prior-art packing material requires laminating a general polyester film with a nylon film, making the production process complicated and costly.